Induction meter



Oct. 16, 1934. EQ PAHN wmsss INDUCTION METER Filed Aug. 11, 1932 K 5 3 1a 1. f I, l I TEFZ I l 9 u h I 1 z a da 7 I I I i? /12" Patented Oct. 16, 1934 & GYIsA- G-s. A of Switzerland Zug, Switzerland, a corporation Application August 11, 1932 Serial No. 628,278

- -In Switzerland Angust 14,1931 7 I 4' Claims. (01," 171-2 4) The present invention relates to induction meters and ,more particularly to temperature compensated inductionwatt hour meters.

7. Objects and advantages of the invention will 5 be set forth in part hereinafter and in part'vvill be obvious" herefrom, or ma be learned by practice with the invention, the same being realized and attained by means of the instrumentalities v and combinations, pointed out in the appended claims.

The invention consistsin the novel parts, coristructions,"arrangements, combinations and improvernents herein shown and described. The accompanying drawing, referred to herein and constituting, a part hereof, illustrates one embodimenfio'f the invention, and tOgethrwith the description, serves to explain the principles of the invention; v I L l Of tliedraWingL- v{2O Figure lie 2'; frag 'entary diagrammatic view of an illustrativeembodimentof the'present vention, and showing theseveral paths of the magnetic flux; and v Figure 2 is, a fragmentary front elevation of the parts ,diagrammatically shown in Figure 1 omitting the current coil and core, The. present invention has for its object the provision 'of improved temperature compensated inductionmeter of the Ferraris type. Another object is the provision of an induction meter in which the temperature compensation is effected by a variation in the reactivity of a secondary current circuit associated with the voltage driving circuit so that the phase distortion between the current flux and the voltage flux remains fairly constant.

It is well known that induction measuring instruments such as Ferraris watt hour meters are subject to temperature errors and generally operate too fast at increased temperatures and too slowly at low temperatures. The temperature errors of these meters are also dependent upon the power factor of the consumer and, as a rule, the temperature error is greater at cos =1 than at cos 4 =0.5.

These temperature errors are due principally to the changes induced in the driving and braking moments of the meter, in consequence of the lowering of the braking 'fiux of the permanent mag- "59 net as the temperature increases and the change in the resistance of the armature as well as by the change in the resistance in the pressure coil. Increases in temperature also cause a diminution in the secondary currents induced by the driving currents in the armature and in the short circuit windings and consequently reduce the ampere windings in phase opposition to the driving currents. These factors react to produce'an increase in the driving currents and a reduction in'a phase displacement of the driving currents,

and likewise the increased resistance of the voltage coilresults in a reduction of the angular phase.

In an efiicient meter for correct registration, the moment of rotation exerted on the armature must be proportional to the power factor and for constant frequency, the following equation may be used: v

D=Cq5rz sin it or D=CEI cos From this equation, it can be seen that at unity power. factor, the temperature error is often brought about by an increase in the driving fluii or a diminution in the braking force. At less than unity power factor, the angular phase as well as the changes in the current plays an importai-it part, the former acting against the latter. With an inductive load, for example, at cos =0.5 thertemp'erature error is les's'tha'n foicos =1.

Inac'cordance with the present embodimentof the invention, the temperature errors referred to above are compensated by means of automatical: ly variable device's producing a variation in the reactivity of the secondary current circuit coupled with the voltage driving force in such a way that the phase distortion between the current flux and voltagedriving flux remains fairly constant. These temperature controlled devices preferably comprise bi-metal strips of magnetic material associated with the pressure or voltage core and adapted to automatically vary the air gap and thereby change the fields and driving fluxes in accordance with changes of temperature.

It will be understood that the foregoing general description and the following detailed description as well are exemplary and explanatory of the invention but are not restrictive thereof.

Referring now in detail to the present preferred and illustrative embodiment of the invention as shown in the accompanying drawing, the

measuring instrument comprises a Ferraris watt provided with a voltage winding 11, supplied with electrical energy at the potential of the circuit being measured. The armature or metering disc 13 is positioned closely adjacent to the lower end of core 5 and is driven by the voltage flux which is in phase displacement with respect to the curring 1 is provided around a mid portion ofbow 2.

At the lower end of bow 2 is provided a bi metal strip 8 formed, at least in part, of mag:

netic material and is secured to said bo w by; means of screw '7. Bi-metal strip 8 extends hori-q zontally beneath the lower end of core '5 and is spaced therefrom a distance sufficient to provide an air gap 12 in which disc 13 moves. 7 I A second bi-metal strip 9, also in partof magnetic material, is attached to the upper portion of bow 2' by screw 10 and extends around short circuiting ring 1, the free end of this bi-metal strip being positioned closely adjacent to the mid portion of bow 2.

The voltage driving flux E produced by the voltage coil 11 on the central leg 5' of the voltage core 5 passes across air gap 12, flows to the bimetal strip 8; which forms a magnetic counterpole, and is then conducted to bow 2. The secj ondary currents induced by the voltage flux E in the short-circuiting ring 1, produce a stray field (155 which flows across air gap'14 and. through bi-metal strip 9. Bi-metal strips 8 and 9 are arranged so that the air gaps 12 and 14 become larger with increased temperature and smaller on areduction intemperature. I

When the temperature rises the magnetic resistance of air gap 12 is'increased and this,together with the reduction in the currents reduces the driving flux. Air gap 14 is similarly enlarged and the reactivity of the short circuit current'in the short circuiting" ring 1 becomes less. -The short circuit current increases and compensates for the reduced angular displacement'betw'een the voltage and current driving fluxes which is caused by diminution in the'current. By proper 7 rent insaid'ring.

dimensioning and positioning of the parts, it is possible to adjust these several conditions so that the temperature compensation is properly effected at all power factors.

The invention in its broader aspects is not limited to the specific mechanisms shown and described but departures may be made therefrom within the scope of the accompanying claims without departing from the principles of the inn vention and without sacrificing its chief advantages.

--What I claim is:-- V '1. In an induction meter having a rotatable metering disc, current and voltage coils and cores, a bimetal counterpole partly of magnetic material in magnetic-conducting relation to the v l a e core, a short circuiting ring encircling saidpi uiltfirpole for producing a stray field and a bimetal strip partly of magnetic material ad- I jacent to said ring for changing the air gap between said strip and counterpole varying the cur- 2. In an induction meter having a rotatable metering disc, current'and voltage coils and cores, amovable counterpolefor said voltage core, a short circuiting'ring encircling said counterpole and a variable magnetic shunt adjacent to said ring and thermally responsive means for" moving said counterpole to change the air gap between it'and the voltage core and varying said shunt to maintain correct metering by said disc. 7 3. ma induction meterh'a'ving a rotatable metering disc, current and voltage coils and cores, a counterpole forming part of a magnetic circuit coupled with the voltage core,fa' short circuiting ring in said circuit, -a magnetic shunt around said ring and; thermally responsive J means for variably positioning'the counterpole and shunt to vary the air gap between the counterpole and voltagecore and between the shunt and counterpole to'maintain constant the phase displacement between the current and voltage driving fluxes.

'4. In an induction meter having a rotatable metering disc, current and voltagecoils and cores, a bow of magnetic material coupled with the voltage core, 'a'bimetal counterpole attached to said bow, a'short' circuitirig ring around said bow and a bimetal partly magnetic shunt adjacent to said ring and coupled to said how. EMIL SPAHN. 

